The invention relates to an apparatus on a drafting system of a spinning room machine, especially a draw frame, carding machine, combing machine or the like, for weighting the drafting system rollers.
It is known to provide, for weighting drafting system rollers, at least one pressure-medium cylinder with a piston which is acted upon by pressure medium and is arranged so as to be axially movable inside a cylinder housing and from which a piston rod extends, the piston rod passing through at least one cylinder cover that defines the cylinder housing at the end, there being an inductive sensor arrangement for determining the position of the piston with the piston rod.
In such a known apparatus (EP 1 428 914 A), a switching disc is frictionally mounted coaxially with the piston so as to be displaceable on the piston rod, which switching disc cooperates with a switch to determine the position of the piston. The switching disc is at least partly permanently magnetic in order to cooperate with an inductive sensor as a switch for determining the position of the piston. If a lap of fibre material then forms around the upper roller, the floating upper roller is pressed in the direction of the pressure-medium cylinder. The presser rod of the pressure-medium cylinder making contact with the upper roller consequently moves in the direction of its retracted end position. When the presser rod is retracted, the switching disc, which is frictionally mounted thereon, connects the switch and the drafting system is switched off. The drafting system can then be opened manually and the lap removed. The drafting system can then be brought into the operating position again by closing the weighting arm. In the known apparatus, the detection of a piston in a very specific position (lap monitoring) is effected by means of an inductive proximity switch. Such an inductive sensor has a closing contact which closes when the piston approaches a previously defined position and accordingly sends a lap monitoring defect signal to the control means. That position must be determined afresh every time the upper rollers are ground. A further substantial disadvantage is that it is not possible to detect the travel of the piston (up and down).